Various suggestions have already been made for producing a wrap-around yarn comprised of a substantially untwisted core yarn, or roving, around which a binder thread is helically wound. Thus, for example, U.S. Pat. No. 3,328,946 illustrates an untwisted core yarn supplied by the rollers of a drafting system being fed through a stationary tube on which is rotatably mounted a bobbin containing the binder or wrap-around thread, the spindle being belt driven. The binding thread coming from the rotating bobbin and, likewise, being introduced into the stationary tube is thus deposited, in the area of the inlet opening of the tube, helically around the untwisted core thread thus strengthening the thread. In order to keep to a minimum the possible breakage of the core yarn, the inlet opening of the tube is arranged at a distance from the supply rollers which corresponds to the average length of the staple fibers in the core thread and an air stream directed against the take-up rollers is introduced into the stationary tube.
This principle is also used in another known method in which the bobbin with the binder thread is arranged on a driven hollow spindle and rotates with the same (U.S. Pat. No. 3,831,369). This has the disadvantage that because of the necessary close positioning of the guide tube or the hollow spindle with respect to the supply rollers, operation of the device is made more difficult and the adjustment of the distance between these parts of the device and the length of fiber to be processed must be matched. Furthermore, the production of turbulent air and the drive of the bobbin for supporting the binder threads and its associated balance problems require additional technical layout and increased operating costs which reduce the economic viability of this yarn production method. A reduction in the economic viability is also brought about by the fact that the imbalances caused by the rotation of the bobbin reduce the package weight of the bobbin.
It has also been proposed to feed the untwisted core thread coming from a pair of rollers through the hollow axle of a false twist spindle and to give it a temporary or false twist by means of a friction ring arranged at the inlet opening of the spindle (DT-PS No. 1,685,881). The binder thread, which is taken off a bobbin arranged coaxially to the false twist spindle and driven by the same, is likewise fed to the inlet opening of the spindle and is helically wound around the untwisted core thread. During the passage through the hollow spindle, the yarn is subjected to a drawing process at the hand of the take-up rollers, which are in the form of drawing rollers, and are finally fed to a take-up bobbin. By means of the false twist which the core thread has been given and which, as a result of the wrap-around process is again undone, the core thread is given sufficient strength prior to wrapping around with the binder thread. The above said disadvantages which result from a driven bobbin, however, are also present in this known solution.
In U.S. Pat. No. 4,028,874, a method for producing a roving is disclosed wherein a filament binder yarn is wound onto a stationary bobbin of small diameter and thereafterwards the binder yarn from the bobbin, together with the fiber band is passed through the hollow bobbin axis, whereby the fiber band is wrapped around by the filament binder. In this case, the number of the windings taken from the bobbin corresponds to the number of the windings applied to the fiber core bands. This means that even in the case of small bobbin diameters and, thus, small package weight, the number of windings which can be placed around the fiber core is limited. Thus, this method is suitable only for the production of a roving which will then have to be subjected to drawing and therefore may only have a strength which will not impair this process.
Accordingly, an important object of the present invention is to provide a method and device which avoids the above disadvantages and in a simple and cost saving manner enables the production of a wrap-around yarn with high output of production and the choice of any number of windings per unit length.